[Luther Spoehr is an HNN Book Editor and Senior Lecturer in Education and History at Brown University.]

For the past 40 years or so, religious voices raised in public debate—think Jerry Falwell, Pat Robertson, and the like--have mainly occupied the conservative side of the political spectrum. (Indeed, as I write, a number of Tea Partiers who oppose raising the debt ceiling because God told them to, seem to be on the verge of falling off the end of that spectrum entirely.) It was not always thus, of course. Martin Luther King, Jr., was only the most prominent ministerial civil rights advocate in the 1960s, and the movement opposing the Vietnam War found much of its rationale from clergy such as William Sloane Coffin and the Berrigan brothers. But before all of them, with writings and lectures that wove philosophical thought and religious conviction as organically and eloquently as any of them, there was Niebuhr.

Reinhold Niebuhr (1892-1971)—theologian, political philosopher, and public intellectual—was a conspicuous, distinctive presence in American political and social debates for over 35 years. With his emphasis on human imperfection and the dangers of the sin of pride, he was a liberal with a difference; his optimism about the possibilities of reform was far more restrained than, say, John Dewey’s, to say nothing of the more self-confident policymakers whom he hoped to influence during his career. An ordained minister, “Christian realist,” and stalwart proponent of “Protestant neo-orthodoxy,” he wrote over a dozen books, including Moral Man and Immoral Society (1932) and The Irony of American History (1952), along with a multitude of articles for general readership in publications such as The New Republic and Life magazine. While at his post in Union Theological Seminary from 1928 to 1960, he founded and edited Christianity and Crisis, a periodical that, in Peter Steinfels’s words, “provoked and guided the liberal wing of American Protestant Christianity” during Niebuhr’s lifetime and beyond. He helped to found the liberal organization that became Americans for Democratic Action. And his influence lingered: his words and ideas have been quoted and cited by political analysts and political leaders, including Jimmy Carter, Hillary Clinton, and both John McCain and Barack Obama. Historians still study him, along with Hans Morgenthau, Walter Lippmann, and George Kennan, and others, as part of a disparate group of “realists” (the word does keep recurring) whose analysis of the Cold War was at the center of foreign policy debates after the end of World War II.

To the extent that the public remembers Niebuhr at all, it is probably for some version of his Serenity Prayer: “God, give us grace to accept with serenity the things that cannot be changed, courage to change the things that should be changed, and the wisdom to distinguish the one from the other.” To the prominent intellectual historian John Patrick Diggins, this is not a sufficient memorial. In his book, completed just before his death in 2009, Diggins makes the case for Niebuhr’s contemporary importance, prompted primarily by Diggins’s concern that under President George W. Bush America, as it had in the past, was overreaching again, this time in Afghanistan and Iraq: “Niebuhr would dismiss the office-seeker,” Diggins says, “who presumes to testify to God’s will. While he thought it was essential that religion play a vital role in public life, he believed its purpose was profoundly cautionary: religion could show Americans how to guard against the temptation to parade their righteousness.”

Readers familiar with Diggins’s The Lost Soul of American Politics (1984) will find this book an almost inevitable extension of that work, in which he called for a “Niebuhrian corrective to the pretensions of American virtue.” His approach is the same as it was in all of his books. In the words of Robert Huberty (Diggins’s former student who was brought in to “review the text, to check facts and footnotes, fill in narrative chinks, and buff away syntactic rough edges”), Diggins did not want merely “to put ideas in historical context, tracing their antecedents and consequences. He was unembarrassed about wanting to know whether our ideas are true and good, and what results from them.” His goal for this particular tract on the virtues of modesty was not a modest one: to open the eyes of policymakers and the public to the need for humility and restraint.

To Diggins, Niebuhr’s ideas are obviously “true and good.” Even people inclined to agree, however, will not necessarily be persuaded by some of Diggins’s occasional attempts to identify historical examples of Niebuhrian politics in action. Probably the most obvious example of this is Diggins’s take on Ronald Reagan (a president about whom Niebuhr, alas, never had a chance to comment). One would think it would be very hard to fit the square peg that is the optimistic Reagan, who insisted it was “morning in America” and happily cast the country as Winthrop’s “city on a hill,” into the round hole of Niebuhrian “realism.” But Diggins tries. He says that during the Cold War, “anticipating initiatives that President Ronald Reagan would implement more than three decades later, Niebuhr urged the United States to engage in personal diplomacy to negotiate nuclear disarmament with the Soviet Union.” Was this Niebuhrian president the same one who moralized about the Soviet Union as the “evil empire,” fantasized about “star wars,” and cheerfully allowed subordinates to flout the law in order to expand American power abroad in the Iran-Contra affair?

Diggins is at least consistent: in his 2007 book Ronald Reagan: Fate, Freedom, and the Making of History he designated Reagan, “after Lincoln, one of the two or three truly great presidents in American history,” and, with Lincoln and Franklin Roosevelt, “one of the three great liberators in American history.” Whether Niebuhr would have agreed with this assessment is hypothetical, to say the very least. It’s certainly not historical. Readers wanting more specific examples of what Niebuhr thought and said about the important issues of his own time are advised to turn to Richard Wightman Fox’s indispensable Reinhold Niebuhr: A Biography (1985).

Diggins rightly stresses how Niebuhr’s studies and his Calvinistic consciousness of original sin and the dangers of pride separated him from more confident avatars of the “American Century.” But even in the shadow of the 20th century’s most horrific events, Niebuhr maintained a philosophical balance between optimism and pessimism that leaned towards hope. In the foreword to The Children of Light and the Children of Darkness (1944), as the terrible costs of World War II mounted and democracy’s future remained uncertain, Niebuhr asserted that “Man’s capacity for justice makes democracy possible, but man’s inclination to injustice makes democracy necessary.”

Like Niebuhr, Diggins has a gift for the pithy, even the aphoristic, that is especially effective when operating in the realm of abstractions. He is at his best when identifying sources of Niebuhr’s thought and comparing his ideas with philosophers from Aristotle and Aquinas to Nietzsche and Kierkegaard. Often he sounds downright Niebuhrian himself, as when he observes that “the essence of the Christian religion is the dialectic between grace and pride.” And he shrewdly comments that “The Irony of American History is not a call to moral clarity but an acknowledgement of moral ambiguity.” But every once in a while, as in his characterization of Reagan, he expects the reader to overlook a truckload of contrary evidence.

Although one can’t know for sure if Diggins might have expanded upon his more tenuous arguments more fully had he lived to see the book through its final editing, it seems safe to say that the essentials of what he wanted to say about Niebuhr are here. And his presentation of Niebuhr’s ideas provides a quick, useful introduction to Niebuhr’s thought. These days, however, although the relevance of Niebuhr’s thought may be obvious, its efficacy is hardly guaranteed. Niebuhr and his Serenity Prayer have been succeeded as discourse by the equivalent of George Costanza’s father and “Serenity now!!” Given the spectacle of our current political quarrels, as America runs helter-skelter after threats real and imagined abroad and debate descends into incoherence at home, it is sobering to consider the possibility that even Niebuhr, the “realistic” apostle of humility and hope, may have been too optimistic about the prospects for American democracy.